Letter pubs.acs.org/OrgLett
Rh(III)-Catalyzed C−H Activation/Cyclization of Benzamides and Diazonaphthalen-2(1H)‑ones for Synthesis of Lactones Renjie Chen and Sunliang Cui* Institute of Drug Discovery and Design, College of Pharmaceutical Sciences, Zhejiang University, 866 Yuhangtang Road, Hangzhou 310058, China S Supporting Information *
ABSTRACT: A Rh(III)-catalyzed C−H activation/cyclization of benzamides and diazonaphthalen-2(1H)-ones for synthesis of lactones has been developed. In the presence of Rh(III) catalysis, the benzamides would form rhodacycle species and could be trapped by diazonaphthalen-2(1H)-ones for arylation, and the following intramolecular lactonization would rapidly furnish the products. Thus, the diazonaphthalen-2(1H)-ones were first revealed as a lactonization component in Rh(III)-catalysis, while the kinetic isotope effect study was conducted and a plausible reaction mechanism was proposed.
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Scheme 1. Rh(III)-Catalyzed C−H Activation/Cyclization between Benzamides and Diazo Compounds
n recent times, Rh(III)-catalyzed C−H functionalization has become a powerful and distinct method for the construction of heterocycles.1 For example, benzamides are versatile building blocks in Rh(III)-catalyzed C−H functionalization and have been widely investigated to couple with alkenes,2 alkynes,3 diazo compounds,4 and boronic acids5 for accessing diverse heterocycles in a convergent manner. For example, the Rh(III)catalyzed coupling of benzamides and diazo compounds was first revealed by Rovis4a in which the diazo compounds acted as a onecarbon component (Scheme 1A). Our group revealed that the vinyl diazo compounds could serve as a three-carbon component in which a 1,3-allylic migration occurs (Scheme 1B).6 More recently, Wang and co-workers reported a Rh(III)-catalyzed annulation of benzamides and diazo compounds for the synthesis of isoquinolones and pyridones, and the diazo compounds served as two-carbon reagents (Scheme 1C).7 Despite these advances, the exploration of Rh(III)-catalyzed coupling of benzamides and diazo compounds with new reaction modes remains interesting and challenging. Diazonaphthalen-2(1H)-ones, a type of unique diazo compound that could rearomatize to naphthalenols in the presence of Rh(II)-catalysis, received less attention than the other diazo compounds.8,9 Continuing our interest in Rh(III)catalyzed C−H functionalization and heterocycle synthesis,6,10 we hypothesized that the diazonaphthalen-2(1H)-ones might be a promising carbenoid reagent to couple with benzamides for delivering interesting products. Herein, we would like to report a Rh(III)-catalyzed C−H activation/cyclization of benzamides and diazonaphthalen-2(1H)-ones for synthesis of lactones (Scheme 1D). We commenced our study by investigating benzamide 1a and 2-diazonaphthalen-1(2H)-one 2a 11 in the presence of [Cp*RhCl2]2 catalysis. When the reaction was conducted in the solvent of CH3CN with Ag2CO3 as an additive at 85 °C © 2017 American Chemical Society
(Table 1, entry 1), only trace product was observed. Variation of Ag2CO3 to Ag2O, AgOTf, and AgBF4 did not show any improvements (entries 2−4). Gratifyingly, when AgOAc was Received: June 8, 2017 Published: July 20, 2017 4002
DOI: 10.1021/acs.orglett.7b01728 Org. Lett. 2017, 19, 4002−4005
Letter
Organic Letters Table 1. Reaction Optimizationa
Scheme 2. Substrate Scopea
entry
additive
solvent
temperature (°C)
yield (%)b
1 2 3 4 5 6 7 8 9 10c 11 12
Ag2CO3 Ag2O AgOTf AgBF4 AgOAc CsOAc Cu(OAc)2 AgOAc AgOAc AgOAc AgOAc AgOAc
CH3CN CH3CN CH3CN CH3CN CH3CN CH3CN CH3CN CH3OH THF toluene toluene toluene
85 85 85 85 85 85 85 85 85 85 50 rt
